Implement the 026-roll-initiative feature that adds d20 roll buttons for bestiary combatants' initiative using a click-to-edit pattern (d20 icon when empty, plain text when set), plus a Roll All button in the top bar that batch-rolls for all unrolled bestiary combatants, with randomness confined to the adapter layer and the domain receiving pre-resolved dice values

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

specs/026-roll-initiative/data-model.md

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+# Data Model: Roll Initiative
+
+## Existing Entities (no changes)
+
+### Combatant
+
+| Field | Type | Notes |
+|-------|------|-------|
+| id | CombatantId | Branded string identifier |
+| name | string | Display name |
+| initiative | number \| undefined | The initiative value (set by manual input OR roll) |
+| creatureId | CreatureId \| undefined | Link to bestiary creature — presence determines roll eligibility |
+| maxHp | number \| undefined | From bestiary or manual |
+| currentHp | number \| undefined | Current hit points |
+| ac | number \| undefined | Armor class |
+| conditions | ConditionId[] | Active conditions |
+| isConcentrating | boolean | Concentration flag |
+
+### Creature (from bestiary)
+
+| Field | Type | Notes |
+|-------|------|-------|
+| id | CreatureId | Branded string identifier |
+| dexScore | number | Dexterity ability score (used for initiative modifier) |
+| cr | string | Challenge rating (determines proficiency bonus) |
+| initiativeProficiency | number | 0 = none, 1 = proficiency, 2 = expertise |
+
+### Initiative Modifier (derived, not stored)
+
+Calculated on demand via `calculateInitiative(creature)`:
+- `modifier = Math.floor((dexScore - 10) / 2) + (initiativeProficiency × proficiencyBonus(cr))`
+- `passive = 10 + modifier`
+
+## New Concepts (no new stored entities)
+
+### Roll Result (transient)
+
+Not persisted — computed at the adapter boundary and immediately applied:
+- `diceRoll`: integer 1–20 (generated via Math.random at adapter layer)
+- `initiativeValue = diceRoll + modifier` (computed by domain function, stored as combatant's `initiative`)
+
+## State Transitions
+
+### Single Roll
+
+```
+Combatant(initiative: any | undefined)
+  → rollInitiative(diceRoll, modifier)
+  → Combatant(initiative: diceRoll + modifier)
+  → encounter re-sorted by initiative descending
+```
+
+### Batch Roll
+
+```
+Encounter(combatants: [...])
+  → for each combatant with creatureId:
+      → rollInitiative(diceRoll_i, modifier_i)
+      → setInitiative(encounter, id, value)
+  → single save with final sorted state
+```
+
+## Validation Rules
+
+- `diceRoll` must be an integer in range [1, 20]
+- `modifier` is any integer (can be negative)
+- Final `initiative` value is any integer (can be negative, e.g., 1 + (−3) = −2)
+- Only combatants with a non-undefined `creatureId` are eligible for rolling